Power distribution to microelectronic devices, such as integrated circuit chips is a major concern in many electronic applications. Of particular concern in the context of the present invention is power distribution to integrated circuits packaged in multichip modules.
In many electronic applications, particularly computer systems, a plurality of individual integrated circuit ("IC") chips are used to perform various system functions. The IC chips, which are quite small, must be "packaged" to provide signal, power and ground connections in a way that prevents damage to the highly sensitive chips. Typically, in low end applications, the IC chips are each individually packaged and then connected to a substrate, such as a computer motherboard. A multichip module ("MCM") is a form of packaging wherein a collection of IC chips are attached to one or more interconnected substrates. Multichip modules are used to improve overall system performance in several ways: the overall space needed to house the IC chips is significantly reduced, and by shortening the distance between chips within the module, high speed device operation is facilitated, e.g., power consumption, interconnect inductance and signal transmission delays are all reduced. MCMs may be designed to incorporate additional features such as an integral IC chip cooling system.
In an MCM a plurality of IC chips are typically connected to a multilayered substrate which contains the signal and power lines needed to supply power and to interconnect the chips to each other and to external devices. The substrate on which the IC chips are mounted will be referred to as the "MCM substrate." The connection between the MCM substrate and the IC chips may either be direct or through an intermediate or "interposer" substrate. In order to make the required number of interconnections, MCM substrates generally contain multiple patterned conductive layers separated by dielectric material. In addition, in order to provide bypass capacitance very close to the integrated circuit chips, capacitors are sometimes embedded within the MCM substrate, since the multilayered structure readily lends itself to capacitor formation, i.e., the capacitors are easily formed from opposing metal layers separated by dielectric. Generally, MCM substrates are either formed from ceramic layers, with metal paste used to form the signal and voltage lines and interlayer vias, or from thin film materials such as copper and polyimide. Hybrid MCM substrates, employing both types of technology are also known in the art. The present invention is particularly useful in connection with thin film MCM substrates, which are becoming more common due to the high density of interconnects they make possible.
Despite performance improvements, known multichip modules have several elements that limit system performance. One important problem with traditional multichip modules is the routing of low impedance power lines through the same layered thin film structure utilized to carry signals to and from the chip. Modem, high density MCM substrates usually comprise a multilayered thin film structure built up layer by layer on a relatively thick, rigid base substrate. A typical thin-film structure comprises interleaved layers of copper and polyimide. Due to technology used to make the thin film structure and the number of metal layers that are typically used, it is necessary to make the metal layers relatively thin. However, the thin metal layers have a relatively high impedance which results in undesired noise, voltage loss and excess thermal energy production, when the thin layers are used to supply power to the IC chips. Increasing the number of layers, which is one way of decreasing impedance without increasing the thickness of the layers, decreases module manufacturing yield.
Fabrication yield is a significant concern in the design and construction of complex multichip modules. In many designs, a failure in any individual component of the module will result in the entire module becoming useless. The fabrication yield of MCM substrates is directly related to the number of layers in the structure and is particularly related to the formation of any embedded bypass capacitors. The capacitors are particularly susceptible to breakdown due to small defects and the thinness of the dielectric layers used to separate capacitor plates.
Accordingly, it is a general object of the present invention to provide a structure for and a method of making a power distribution system for microelectronic components mounted on a chip substrate that improves over the prior art.
Another object of the present invention is to improve the routing of signal and power lines to microelectronic components mounted on a multilayered substrate.
Still another object of the present invention is to provide improved low impedance means for delivering power to microelectronic components mounted on a multilayered substrate.
Another object of the present invention is to provide a structure and method of fabricating a multilayered microelectronic device substrate that minimizes the internal stress of the resulting substrate assembly as it is thermally cycled.
A further object of the present invention is to provide reliable bypass capacitance positioned in close proximity to an integrated circuit chip mounted on a chip substrate.
Yet another object of the present invention is to provide a substrate structure that is highly modular, and a method for fabricating the same, so that individual components can be pretested prior to final fabrication of the substrate, and such that at least some of the components can be repaired.